Listeria spp. are Gram-positive intracellular pathogens that cause severe food-borne diseases in humans. Their pathogenic strategy entails the regulated export of a series of virulence determinants that induce internalization by host cells, phagosomal escape and intracellular cell- cell spreading. However, little is known about the mechanisms for protein secretion in Gram-positive bacteria and no specialized secretion machine for the export of virulence factors has yet been identified. In light of our lack of understanding of these processes, this proposal will address the following questions: 1. What are the Listeria genes required for the secretion of virulence factors? 2. Are there specialized secretion mechanisms responsible for that secretion of virulence factors? Listeria is an excellent model organism for these studies as many molecular and cellular tools are available. The almost complete Listeria genome and availably of relevant animal models will further help us understand Listeria pathogenesis and its interaction with the host. Better understanding of Listeria secretion mechanisms may help us in the identification of better anti-microbial targets, and the development of intracellular delivery vectors for antigens in the fight of not only microbial diseases, but that of human diseases as well.